The term QRP generally refers to making contacts with other Hams while using 5W or less of transmitter power. The difference between 5W and 100W is 13dB, and since a change of one S-unit is defined as a 6dB change in received signal strength; the perceived drop in receive signal level when changing from 100W down to 5W is only slightly more than 2 S-units.
As shown above, the 13dB loss incurred by reducing power from 100W to 5W is compensated for by the 13dB gain in power density.
A drop in signal strength of 2 S-units can make quite a difference in "wide band" communications such as SSB voice, but when using "narrow band" communications such as CW (or some narrow digital systems such as PSK31), reliable 2-way communications can easily be maintained - even at only 5W of power. This is why QRP is often synonymous with CW communications.
QRPers often reduce their chances of making QSOs by using less than optimal antenna systems. If you don't want to become disillusioned by QRP early in the game, always use a good antenna such as a full sized dipole, inverted-vee or vertical strung up as high as possible. This is especially important during periods of poor propagation when even 100W doesn’t net many QSOs if you don't have a really good antenna system. So don't get frustrated with QRP - work the stations you can work, occasionally throw your call out to the DX stations you can hear, and celebrate if one of them hears you. Always be on the lookout for ways to improve your antenna system.
